<!DOCTYPE html>
<html lang="zh-cn">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .container {
      width: 300px;
      display: flex;
      justify-content: space-between;
    }

    .red-green-light {
      display: flex;
      flex-direction: column;
      justify-content: space-around;
      align-items: center;
      width: 70px;
      height: 240px;
      background-color: #333;
      border-radius: 5px;
    }

    .light {
      width: 60px;
      height: 60px;
      border-radius: 50%;
      background-color: #fff;
    }

    .red-green-light .light:nth-child(1).active {
      background-color: red;
    }

    .red-green-light .light:nth-child(2).active {
      background-color: green;
    }

    .red-green-light .light:nth-child(3).active {
      background-color: goldenrod;
    }
  </style>
</head>

<body>
  <div class="container">
    <div class="red-green-light">
      <div class="light red"></div>
      <div class="light green"></div>
      <div class="light yellow"></div>
    </div>

  </div>
</body>

<script>
  // 让灯亮的方法
  const openLight = node => node.classList.add('active')

  // 让灯灭的方法
  const offLight = node => node.classList.remove('active')

  const red=document.querySelector('.red')
  const green=document.querySelector('.green')
  const yellow=document.querySelector('.yellow')

  function light(color,delay){
    return new Promise((resolve,reject)=>{
      openLight(color)
      setTimeout(()=>{
        offLight(color)
        resolve()
      },delay)
    })
  }

  async function show(){
    while(true){
      await light(red,3000)
      await light(green,2000)
      await light(yellow,1000)
    }
  }
  show()


</script>

</html>